Water conservation in irrigation can increase

water use
Frank A. Warda,1 and Manuel Pulido-Velazquezb
aDepartment of Agricultural Economics and Agricultural Business, New Mexico State University, Las Cruces, NM 88003; and bDepartment of Hydraulic and
Environmental Engineering–Institute of Water and Environmental Engineering, Universidad Politécnica de Valencia, Cami de Vera s/n 46120 Valencia, Spain

Edited by Partha Sarathi Dasgupta, University of Cambridge, Cambridge, United Kingdom, and approved September 23, 2008 (received for review
June 10, 2008)

Climate change, water supply limits, and continued population uses outside agriculture (16, 17). Numerous public policies have
growth have intensified the search for measures to conserve water been implemented and billions of dollars in public and private
in irrigated agriculture, the world’s largest water user. Policy investments spent to promote water conservation in irrigated
measures that encourage adoption of water-conserving irrigation agriculture. However, many of these investments have not made
technologies are widely believed to make more water available for additional water available to new users. Although water conser-
cities and the environment. However, little integrated analysis has vation intentions carry considerable political weight, there is all
been conducted to test this hypothesis. This article presents results too often little serious evidence on conservation outcomes that
of an integrated basin-scale analysis linking biophysical, hydro- would be produced by water conservation programs in policy
logic, agronomic, economic, policy, and institutional dimensions of debates, funding opportunities, and the popular press. More-
the Upper Rio Grande Basin of North America. It analyzes a series over, studies that connect water use efficiency with wet† water
of water conservation policies for their effect on water used in savings are rare. Notable exceptions include the works of
irrigation and on water conserved. In contrast to widely-held Hussain et al. (16), Huffaker and Whittlesey (17), Peterson

ECONOMIC
SCIENCES
beliefs, our results show that water conservation subsidies are and Ding (18), Huffaker and Whittlesey (19), and Schierling
unlikely to reduce water use under conditions that occur in many et al. (20).
river basins. Adoption of more efficient irrigation technologies This contribution of this article is to analyze agricultural water
reduces valuable return flows and limits aquifer recharge. Policies conservation subsidies with respect to their effect on water used
aimed at reducing water applications can actually increase water in irrigation and on conserved water available for other uses. A
depletions. Achieving real water savings requires designing insti- basin-scale hydroeconomic optimization model is presented
tutional, technical, and accounting measures that accurately track linking biophysical, hydrologic, agronomic, economic, policy,
and institutional dimensions of the Upper Rio Grande Basin of

ENGINEERING
and economically reward reduced water depletions. Conservation
programs that target reduced water diversions or applications North America (the Basin), shown in supporting information
provide no guarantee of saving water. (SI) Fig. S1. Results of that model are used to examine farm
income-maximizing choices regarding crop mix, irrigation tech-
agriculture 兩 sustainability 兩 institutions 兩 hydrology nology, water demand, consumptive use, return flows, income,
and taxpayer costs of a water-conserving program. The cost
effectiveness of a range of conservation subsidy arrangements
E asterling (1) recently observed that a great challenge facing
21st-century political and scientific leaders will be to increase
the world’s food supply to accommodate a world growing to 10
for reducing water depletions is also identified.

Materials and Methods

billion or more people while also facing climate change. Water Water Conservation. Evapotranspiration (ET) from the watershed’s surface is
in the right quality, amount, time, and place is essential for the depletion‡ or loss of water from a hydrologic basin associated with plant
ecosystems and for economies. Much of the world’s food pro- water use. Water diverted from its natural course through a canal, pipe, or
duction depends on water for irrigation. Natural ecosystems are other conveyance measure and applied in irrigation in excess of ET is not lost
adapted to stream discharge, precipitation, and evaporation because it returns into the basin from which it was withdrawn via surface
patterns. So, adjustments in the water cycle to climate, weather, runoff or deep percolation. This water can be available to other users at other
and land-use change will have large and complex effects on
economic and ecological systems
Author contributions: F.A.W. and M.P.-V. designed research, performed research, contrib-
Many countries have inadequate water supplies to meet their uted new reagents/analytic tools, analyzed data, and wrote the paper.
current urban, environmental, and agricultural needs. In the face
The authors declare no conflict of interest.
of increased water scarcity, population and water demands
This article is a PNAS Direct Submission.
continue to grow (2, 3). The challenge is to grow enough food for
Freely available online through the PNAS open access option.
2 billion more people over the next 50 years while supplying
growing urban and environmental needs for water (4, 5). Some This article contains supporting information online at www.pnas.org/cgi/content/full/
0805554105/DCSupplemental.
analyses have estimated that 60% of added food required will 1To whom correspondence should be addressed. E-mail: fward@nmsu.edu.
come from irrigation (6). Raising food production to support this
*Many definitions of irrigation efficiency have been proposed (14, 15). For this article,
larger world population requires sustaining improved perfor-
efficiency is the ratio of water depleted by plant evapotranspiration (ET) to water diverted
mance of irrigation (7–12). from the stream. ET is the consumed fraction of water diverted. As technologies or
As pressure mounts for irrigated agriculture to produce more management practices are adopted that bring the ratio closer to 1, irrigation efficiency
crop per drop, there is a widespread belief in environmental and increases. Much of this article focuses on what happens to the nonconsumed fraction.

water policy circles that if irrigators made more efficient use of †The term wet water savings refers to real water compared with paper water, i.e. water
rights.
water then there would be more water for environmental uses
‡Some writers prefer the term ‘‘consumption’’ to ‘‘depletion,’’ because depletion suggests
and for cities (12, 13). More than a billion people worldwide lack
the unsustainable action of drawing down on a stock (22). By contrast, consumption occur
safe affordable drinking water (8). A considerable number of as a part of sustainable income. We use the term depletion because it contrasts with water
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informed individuals, large development organizations, and diverted from the stream or water applied to the crop. Water diverted and water applied
much popular belief subscribes to the view that measures to can return to a closed hydrologic basin. Depletion cannot.
increase irrigation efficiency* will result in additional water for © 2008 by The National Academy of Sciences of the USA

www.pnas.org兾cgi兾doi兾10.1073兾pnas.0805554105 PNAS 兩 November 25, 2008 兩 vol. 105 兩 no. 47 兩 18215–18220

 Table 1. Crop water use, price, yield, and cost per acre, Lower Rio Grande, NM, 2006
Production cost
Production cost (100% capital
(0% capital drip drip irrigation
Water Deep Yield, irrigation subsidy), subsidy),
applied* ET* percolation* Price quantity/acre† $/acre/year $/acre/year‡

Crop Flood Drip Flood Drip Flood Drip $/Unit Yield units Flood Drip Flood Drip Flood Drip

Alfalfa 5.0 2.7 2.2 2.7 2.9 0.0 130.00 Tons 8.0 10.0 884 1,357 884 993
Pima cotton 2.8 1.5 1.2 1.5 1.6 0.0 1.05 Lbs 750.0 937.5 979 1,324 979 960
Upland cotton 2.8 1.5 1.2 1.5 1.6 0.0 0.75 Lbs 1,000.0 1250.0 1027 1,261 1027 897
Spring lettuce 2.5 1.4 1.1 1.4 1.4 0.0 5.84 Cartons 475.0 593.8 3001 4,398 3,001 4,034
Fall lettuce 3.3 1.8 1.4 1.8 1.9 0.0 6.23 Cartons 500.0 625.0 2,638 3,971 2,638 3,606
Fall onions 4.7 2.5 2.0 2.5 2.7 0.0 6.63 Sacks 1,200.0 1500.0 5,762 8,848 5,762 8,484
Midseason onions 4.0 2.9 2.3 2.9 1.7 0.0 6.38 Sacks 675.0 843.8 3,722 5,708 3,722 5,344
Spring onions 4.8 3.4 2.7 3.4 2.0 0.0 6.43 Sacks 825.0 1031.3 4,455 6,871 4,455 6,506
Grain sorghum 2.0 1.1 0.9 1.1 1.1 0.0 3.70 Cwt 40.0 50.0 615 728 615 364
Wheat 2.5 1.4 1.1 1.4 1.4 0.0 3.75 Cwt 92.0 115.0 718 929 718 565
Green chile 4.6 2.5 2.0 2.5 2.6 0.0 285.00 Tons 11.0 13.8 2,275 3,356 2,275 2,992
Red chile 5.0 2.7 2.2 2.7 2.9 0.0 0.72 Lbs 3,500.0 4,375.0 2,004 2,851 2,004 2,486
Pecans 6.0 3.2 2.6 3.2 3.4 0.0 2.28 Lbs 1,158.1 1,447.7 1,731 3,114 1,731 2,750

*Acre-feet per acre per year.

†Each crop is specified to have a linear relationship between water use (ET) and crop yield across irrigation technologies.
‡Includes annualized cost per acre of drip irrigation, operation, and maintenance.

times in other locations.§ One user’s water inefficiency often serves as the under flood irrigation, although that cost elevation is considerably reduced as
source of another user’s water supply. the public subsidy of drip irrigation increases from 0 to 100%.
On-farm adoption of drip irrigation is one measure widely believed to
conserve water. Drip irrigation allows for precise application of water into Modeling Framework. The hydroeconomic analysis developed for this article is
plants’ root zones, with little loss to runoff or deep percolation. A linear a basin-scale accounting of the Basin’s essential hydrologic relationships,
relationship is typical between ET and crop yield over a wide range of crops institutions, and economic sectors. This integrated model is formulated as a
and water applications (21). So, irrigation technologies that apply water at mathematical optimization problem. The objective is the sum of net economic
optimal times and locations in plant root zones increase crop consumptive use benefits¶ from basin water diversions, for off-stream uses, and for net benefits
of water and crop yield as irrigation efficiency increases. When yield goes up, of water environments. The objective is to maximize the discounted value of
ET typically rises. net economic benefits over a 20-year time horizon. Constraints are used to
Water losses through deep percolation or surface runoff will be reduced, characterize the basin’s hydrology and its institutions. Our basin-scale ap-
possibly to nearly 0, through drip technology, but more ET will be used by the proach extends similar previous work by Vaux and Howitt (24), Booker (25),
plant in supporting its reduced plant stress and higher yield. More efficient and Hurd et al. (26), all of whom developed integrated basinwide hydrologic
irrigation systems reduce diversions from streams and increase crop both yield models for policy analysis containing an economic objective.
and gross revenue (18). Depending on the cost of installing drip irrigation, The model is formulated and solved on an annual time step, with reservoir
costs and returns of production, and the price of water, the farmer who uses storage and other hydrologic and economic conditions carried forward to
each next time period. Fig. S2 shows a schematic of the basic hydrologic–
the technology may experience increased yield and higher income per unit of
agronomic balance at the field-stream level. Mathematical documentation of
land. From the farmer’s economic view the new water-conserving technology
earlier versions of the model has been published elsewhere (27, 28). Although
is good. However, basin-level consumptive use of water can increase.
the model and its documentation were developed for the Basin, it was
designed to be adaptable to other basins, cultures, and economic environ-
Study Area. The Basin is that part of the area drained by the Rio Grande and
ments that characterize the economic value of water.
its tributaries that flow from its headwaters to ⬇70 miles south of the border
cities of El Paso, TX and Ciudad Juárez, Mexico (Fig. S1). Surface water from the
Hydrology. Basin hydrology is based on the principle of water mass balance,
river meets the primary water needs of Albuquerque, NM, El Paso, and Juárez.
defined in both flows and stocks. The most important flows tracked by the
In addition, it serves 1 million acres of irrigated land in the U.S. and Mexico. In
model include headwater flows, streamflows at the basin’s important stream
fall 2004, water storage in Elephant Butte, the largest reservoir in the Basin, gauges, water diverted, water applied to crops, water depleted, reservoir
was ⬍5% of capacity. After an unprecedented 25-year period of full-water releases, groundwater pumping, seepage to aquifers, return flows to streams,
supplies, water allocations during 2003 were reduced to just one-third of reservoir evaporation, and reservoir releases. Important stocks include reser-
full-supply conditions. voir and aquifer levels. A hydrologic mass balance for both surface water and
groundwater is enforced for all flows and stocks. The model includes major
Data. Table 1 shows the most important hydrologic, agronomic, and economic functions that influence any of the flows described above. The mass balance
data for irrigated agriculture used by our analysis. Depending on the crop, for reservoir stocks is given by starting storage minus reservoir releases plus
water applied under drip irrigation is approximately half as much as under river inflows to the reservoir minus evaporation. Changes in any period’s
flood irrigation. However, crop ET is higher under drip irrigation, which groundwater stock are represented through effects of seepage, water ap-
reflects higher water depletions that support the typically greater yields plied, and water pumped.
experienced by irrigators who use this technology. ET under flood irrigation
is typically less than half of water applied; the rest either seeps to deep Institutions. The U.S.–Mexico Treaty of 1906 is an important international
percolation or returns to the stream as surface return flow. The table also treaty. Under it, the U.S. is obliged to deliver 60,000 acre-feet per year to
shows that production costs per acre are typically much higher under drip than Mexico at the El Paso–Ciudad Juárez border. Historically, in severe drought
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§A fraction of water diverted in a basin may return to the basin too late, too far away, or ¶Excluded are costs associated with the public subsidy of drip irrigation’s capital cost. From

in too low a quality to be of economical use or because the water flows into an irretrievable a national view, a public subsidy incurs opportunity costs because those resources typically
sink such as the ocean or saline lakes (23). have alternative uses.

18216 兩 www.pnas.org兾cgi兾doi兾10.1073兾pnas.0805554105 Ward and Pulido-Velázquez

 periods, U.S. deliveries to Mexico have fallen below 60,000. Nevertheless, our Variable costs vary with the scale of the irrigation enterprise (e.g., acres)
model enforces a good-neighbor policy by requiring delivery of 60,000 acre- and with the management decisions made, such as the type of field or
feet to Mexico in all conditions. irrigation technology chosen. They also vary with the intensity of any single
Various U.S. Federal laws affect use of the Basin’s water. Our model input on a given land unit. Variable costs occur because of the decision to
enforces the Endangered Species Act of 1973 (ESA), which allocates the Basin’s purchase additional inputs for use in production. In the long run, all costs are
water to produce sufficient streamflow in the San Acacia reach of the Rio variable in the sense that given a long enough period, they can be varied. In
Grande (Fig. 1) to protect from extinction the endangered Rio Grande silvery the short run, such as a single year, revenues must exceed variable costs, or it
minnow. The model enforces this constraint by requiring streamflows at the is more profitable to cease production. Shutting down is always a choice for
San Acacia gauge to exceed 240,000 acre-feet per year. an irrigator facing growing water scarcity. At a point in time near the end of
In the western U.S., numerous interstate compacts have been signed since the irrigation season, nearly all costs are fixed in the sense that they have
1922 signing of the Colorado River Compact. The Rio Grande Compact (the already been incurred, so the incremental revenue coming in from a crop is
Compact), signed in 1938 by Colorado, New Mexico, and Texas, divides the likely to be considerably higher than the additional variable costs needed to
river’s annual flow among those states. It obliges each upstream state to make harvest the crop.
larger annual deliveries to the downstream state in wetter periods. Each state Other costs. For urban areas, there are considerable costs for purification to
receives a specified percentage of headwater flows, so the Compact spreads make the water safe and healthy for human consumption. Treatment costs are
the risk of drought or climate change among the three states. Our model considerably higher than for agriculture, but urban treatment costs are typ-
allocates water among the states according to the Compact’s written rules. ically lower for pumped water than for diverted river water. Urban delivery
In many of the world’s water-stressed regions, neighbors have agreed to cost data were obtained from the Albuquerque and El Paso water utilities, and
share scarce supplies in drought periods. Since the early 1950s, the New Mexico agricultural water cost data were obtained from published farm enterprise
and Texas have agreed to share water delivered by the Rio Grande Project. cost and return budgets. Both urban and environmental costs are included in
Based on historical agricultural acreage in production in southern New Mexico the objective function as negative terms when costs are subtracted from
and Texas at the time of the Project’s construction, U.S. lands in New Mexico benefits.
receive up to 57% of any year’s allocation, and lands in Texas have received up Net environmental benefits are measured as gross environmental benefits
to 43%. minus added gross environmental management costs needed to assure a
higher quality environment. Data are scarce on costs of managing the water
Economics. Benefits. The model’s economic analysis accounts for both water environment. As a first approximation, we measured those costs as manage-
ment costs incurred by the New Mexico State Parks Department for maintain-

ECONOMIC
use-related benefits and the benefits of a higher-quality water environment.
Benefit functions were developed to approximate water users’ willingness to ing fishing facilities and for supporting larger numbers of anglers in the face
pay for water-related services. The two urban water-use nodes in the model of reservoir volume increases.
are Albuquerque and El Paso. For both of those cities, the value of water is Discounted net benefits. Discounted net present value is expressed in its stan-
measured by water’s price times the number of units sold to its customers plus dard algebraic form:

冘冘 冘冘
any related consumer surplus. Consumer surplus is measured as the area
beneath the urban water demand function and above actual price charged. NBuut NBeet
NPV ⫽ ⫹ [1]
For environmental benefits, willingness to pay is measured as the maximum 共1 ⫹ ru兲t 共1 ⫹ re兲t
u t e t
price that could be charged to visitors at the Basin’s six major reservoir-based

ENGINEERING
recreation sites.储 More details on the economics of urban and environmental
where the u and t indices refer to benefits and costs of water use and the water
values are presented in refs. 27 and 28.
environment, respectively; ru and re are rates for discounting water uses and
Irrigation benefits. The agricultural analysis is based on estimating how
water environments; and NBut and NBet are net benefits from water uses and
income-optimized cropping practices adjust to various subsidies of drip irri-
water environments. Water use in the Upper Basin is heavily constrained by
gation. The agricultural analysis of water is based on estimating how acreage
scarce water supplies and by existing institutions. The four existing institutions
in production by crop and irrigation technology adjusts to various capital cost
described earlier are incorporated into the model. The discounted net present
subsidy levels of drip irrigation, ranging from 0 to 100%. As is common
value includes the summed stream of net use-related benefits and net envi-
worldwide, drip irrigation in the Basin is considerably more expensive than
ronmental benefits. Total basinwide economic benefits defined in this way are
flood irrigation. It also requires less water applied per acre and produces
maximized subject to the constraints defined by hydrology and water alloca-
greater crop yields. The answer to the question of whether or not drip
tion institutions described above. The objective as well as those water alloca-
irrigation is economically attractive to irrigators turns on what combination of
tions and system operations that serve to maximize it are based on standard
economic and water supply conditions make it profitable to choose drip over
microeconomic welfare economics. Similar economic optimization models at
flood irrigation.
the basin scale are described by Booker and Young (31), Draper et al. (32),
Irrigators’ choices are based on what provides the highest discounted net
Pulido-Velázquez et al. (33), and Booker et al. (34).
present value of farm income. Agronomic– economic data include price by
crop, production cost and yields per acre by crop and irrigation technology,
Solving the Model. We formulated the model as a dynamic nonlinear optimi-
and total acres in production. The hydrologic relations included ET, water
zation model, for which the objective was to maximize discounted net present
applied, deep percolation, and surface return flow per acre by crop and crop
economic value summed over water uses, water environments, irrigation
irrigation technology. The Basin’s water supply is defined by average historical
technologies, locations, and time periods. In the model, reservoir contents,
headwater flows as well as reservoir and aquifer starting conditions for 2006.
pumping, water use patterns, and on-farm irrigation technologies are opti-
Other benefits. The basinwide model identifies water use patterns and
mized over the model’s time horizon, in which the hydrologic input is head-
water decisions that maximize discounted present value of net benefits. The
water inflows as well as starting values for reservoir and aquifer levels. The
model was designed to identify water use patterns that maximize the dis-
model accounts for physical interactions among uses (irrigation, urban, and
counted net present value of economic benefits over water uses, locations,
environmental), storage (reservoirs and aquifers), flows (diversions, pumping,
and time periods. Part of that total basin-scale net benefits includes farm
water applied, water depleted, and return flows), and losses (field, convey-
income as described above. Gross benefits are defined for urban, agricultural,
ance, and reservoir evaporation).
and environmental uses. Although the major focus of this article is the
economics of water conservation in agriculture, the model views agriculture Results
as only one of three water uses (29, 30).
Costs. Production costs of irrigated agriculture. Increased stream diversions or Table 2 shows hydrologic impacts for the river, farm, and aquifer
depletions typically require additional costs to be incurred to make suitable associated with various levels of public subsidies of drip irriga-
for human use the increased water used. For agricultural groundwater- tion. Impacts shown in the table are limited to the 89,000 acres
pumping nodes, the largest incremental costs are those incurred for energy served by the Elephant Butte Irrigation District (EBID) of
and for related operation, and maintenance. Costs are broken into variable southern New Mexico. The base case is defined by a policy of 0
and fixed costs, described below.
subsidy. Under this scenario, farmers are predicted to apply
364,000 acre-feet, of which pumped groundwater supplies 91,000
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储Important excluded environmental values include benefits produced by instream flows at

acre-feet. Some acreage of all 13 crops shown in Table 1 enter
nonreservoir nodes and any environmental values, such as option, existence, or bequest the optimal solution under at least some of the public subsidy
values influenced by variations in reservoir levels or by other water decisions. levels. For the base case, these include alfalfa on 18,760 acres,

Ward and Pulido-Velázquez PNAS 兩 November 25, 2008 兩 vol. 105 兩 no. 47 兩 18217
 Table 2. Water conservation in irrigated agriculture for selected drip irrigation subsidies, Lower Rio Grande, NM, annual average,
2006 –2025, hydrologic outcomes
Hydrologic outcomes, 1,000 acre-feet/year

On farm River

Reservoir Surface Downstream Aquifer,

Subsidy, Subsidy, Water Water release, Stream return Aquifer outflow delivery change in Total water
% capital* $/acre/year† applied ET Pumped inflow diversions flow (river gains if ⬎0) (outflow) storage conserved

0 0 364 167 91 555 273 0 32 314 74 0.0

10 36 371 171 86 566 285 0 34 315 80 ⫺3.7
20 73 362 168 87 558 274 0 32 316 75 ⫺0.6
30 109 328 176 56 555 272 0 29 312 67 ⫺8.5
40 146 318 181 51 549 268 0 26 307 61 ⫺13.6
50 182 318 187 52 533 267 0 24 290 56 ⫺19.5
60 219 319 197 58 534 262 0 19 292 45 ⫺29.6
70 255 324 203 66 532 258 0 17 291 39 ⫺35.9
80 291 324 203 64 535 259 0 17 292 39 ⫺36.0
90 328 324 203 69 513 255 0 15 273 36 ⫺36.0
100 364 324 204 63 535 261 0 17 292 40 ⫺36.7

*Total costs include Program Cost of Water Conservation subsidy.

†Total costs exclude Program Cost of Water Conservation subsidy.

pima cotton on 3,216 acres, upland cotton on 8,218 acres, fall An important finding is that as the subsidy increases, water
lettuce on 4,467 acres, onions on 3,573 acres, wheat on 1,072 depletion never falls below base-level depletion. As the subsidy
acres, green chile on 2,680 acres, red chile on 2,680 acres, and increases, the ratio of depletion to water diverted from the
pecans on 25,906 acres. Under that base case, total optimized stream increases. The ratio of depletion to water diverted rises
agricultural income is $34.1 million per year. Under the optimal to 80% under a 100% subsidy from a base case of 61%, while
base case solution, flood irrigation is used for ⬇90% of the water pumped is reduced from 91,000 acre-feet to 63,000
service area in actual production with drip irrigation used for just acre-feet.
⬍10%. This corresponds approximately to actual 2006 EBID Table 3 shows land use and economic outcomes produced by
conditions. the same drip irrigation subsidy scenarios. Results show that as
We identified effects of a range of cost-sharing arrangements subsidy levels increase, net farm income increases from $34.1
by varying the proportion of the average annualized irrigation million under the base case to $45.5 million under the highest
system improvement capital cost paid by the public agency versus subsidy. At the 100% subsidy, level drip irrigation is used for
the farmer. That part of capital cost paid by the public agency 46,000 of 87,000 acres in production, or 53%. Overall, results
was parametrically increased from 0 to 100% in 10% increments. suggest that a water conservation subsidy policy is unlikely to
Table 2 shows the hydrologic outcomes of 10 scenarios reduce water depletions under any of the scenarios. In fact, water
associated with alternative drip irrigation subsidy levels. The depletions, yields, and acreage are all predicted to increase if
unconsumed part of irrigation water diverted from the stream is total water use is not constrained to base levels by the various
presumed fully available for other uses, either for downstream water authorities. If total irrigated acreage is also allowed to
increase, the potential increase in water depletions is even
surface water use or as aquifer recharge that would be available
higher. We conclude that in river basins where downstream users
for use in current or future periods. Drip irrigation produces
and future generations depend on the unconsumed portion of
higher ET than flood irrigation, while also producing higher crop
diversions in the form of returns to the stream and raised aquifer
yields. Raising the subsidy on drip irrigation induces more drip
storage, subsidies for conservation technology investments are
acreage and more total acreage into production when the Basin’s
unlikely to bring about a new supply of water but will likely lead
reservoirs start very low as they were in early 2006. Total water to increased depletions.
applied (pumped plus diverted) falls from 364,000 acre-feet Results of Table 3 show that subsidies do encourage a shift to
under the baseline to 324,000 under a 100% capital subsidy. more water-efficient technologies. By paying for a part of the
Surface return flows are always 0. Groundwater pumping for capital cost, the program reduces farmers’ irrigation costs.
irrigated agriculture falls considerably, from 91,000 under base- Because of reductions in water applied to crops, increased
line to 63,000 under maximum subsidy. Aquifer-to-river gains fall program subsidies also lead to savings in other variable costs,
from 32,000 acre-feet under baseline to 17,000 under the highest including energy and groundwater pumping. As the subsidy rises
subsidy. Aquifer storage gains fall from 74,000 acre-feet under and as its implementation promotes a change in technology,
no subsidy to 40,000 under maximum subsidy. The net effect results show continued reductions in water applied to crops. At
overall is greater water depletion (greater ET), which produces the same time, net farm income increases because of the subsidy
a negative conservation of ⬇36,700 acre-feet per year under the itself and because of the subsidy’s impact on altered technology
highest subsidy compared with a defined 0 conservation with no and increased crop yields.
subsidy. We find that a progressively increasing public subsidy of Table 3 presents 5 indicators of total economic benefits in
drip irrigation considerably reduces water applied to farmlands. addition to farm income and program cost: These indicators
However, it increases overall water use. These findings support include (i) net benefits of water use including costs of irrigation
the conclusions of Schierling et al. (20) as well similar findings subsidies in total costs (national view); (ii) net benefits of water
published by Huffaker (35), Huffaker and Whittlesey (19), and
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use excluding the irrigation subsidy cost (basin view); (iii) net
Ahmad et al. (36). They also concur with the recent conclusions benefits produced by the water environment; (iv) total net
of Molden (37). benefits of water use plus benefits of the water environment

18218 兩 www.pnas.org兾cgi兾doi兾10.1073兾pnas.0805554105 Ward and Pulido-Velázquez

 Table 3. Water conservation in irrigated agriculture for selected drip irrigation subsidies, Lower Rio Grande, NM, annual average,
2006 –2025; land use and economic outcomes
Land use outcomes (1,000 acres/year) Economic outcomes ($1,000/year)

Land in Land in Total land Net benefits Net benefits Net benefits
Subsidy, Subsidy, drip flood under Farm Program from water from water from water Total net Total net
% capital $/acre/year irrigation irrigation irrigation income cost use A* use B† environment benefits A* benefits B†

0 0 7 68 75 34,102 0 519,848 519,848 23,273 543,121 543,121

10 36 8 69 77 34,723 309 520,211 520,519 22,465 542,676 542,985
20 73 9 66 76 34,770 690 519,826 520,517 23,204 543,030 543,720
30 109 25 52 77 35,242 2,794 518,190 520,984 23,253 541,443 544,238
40 146 32 47 79 36,219 4,613 517,348 521,961 23,313 540,661 545,274
50 182 36 45 81 37,499 6,475 516,686 523,161 22,877 539,564 546,038
60 219 42 42 84 38,903 9,185 515,514 524,699 22,807 538,322 547,506
70 255 45 42 87 40,473 11,422 514,848 526,269 22,821 537,668 549,090
80 291 45 42 87 42,171 13,131 514,836 527,968 22,775 537,612 550,743
90 328 45 42 87 43,632 14,773 515,446 530,219 23,046 538,492 553,265
100 364 46 42 87 45,506 16,571 514,663 531,234 22,795 537,458 554,029

*Total costs include Program Cost of Water Conservation subsidy.

†Total costs exclude Program Cost of Water Conservation subsidy.

including subsidy costs (national view); and (v) total net benefits erably since the mid 1980s. Those increased yields coupled with
of water use plus the water environment excluding subsidy costs changing irrigation practices have worked to increase overall

ECONOMIC
(basin view). This last economic indicator is the objective water depletions.**
function maximized for this analysis. Our findings also suggest that where return flows are an
An important trend is the nearly uniform increase in the important source of downstream water supply, reduced deliver-
Basin’s total net benefits with rising irrigation subsidies. Total ies from the adoption of more efficient irrigation measures will
net benefits from the Basin’s view increase from about $0.543 redistribute the basin’s water supply, which could impair existing
billion per year with no subsidy to about $0.554 billion per year water right holders who depend on that return flow. Our results
under a 100% subsidy, as farm incomes in the Basin increase indicate that water conservation subsidies will not provide

ENGINEERING
from $34.1 million with no subsidy to $45.5 million with a 100% farmers with economic incentives to reduce water depletions and
subsidy. From the national view, the story is different. Where the therefore are unlikely to make new water available for alterna-
taxpayer’s cost of the irrigation subsidy is included in total costs, tive uses. In fact, depletions are likely to increase as a result of
national net benefits fall from a high of $0.543 billion with no subsidies. Drip irrigation is important for many reasons, includ-
subsidy to a low of $0.537 billion with a 100% subsidy. So, ing greater water productivity and food security (12, 15), but
although the irrigation water conservation subsidy is economi- does not necessarily save water when considered from a basin
cally good for the Basin, it is a weak economic performer for the scale (37).
nation. What measures can be taken to promote real water savings?
A first step could be accurate accounting of basinwide water use.
Conclusions Water accounting analyzes use, depletion, and productivity of
Lubchenco (38) described a social contract between science and water at the basin scale (37). Accurate accounting and measure-
society, in which advances in science inform society’s important ment of water use can help identify opportunities for water
decisions. Her observations certainly characterize the elusive savings, increase water productivity, and improve the rationale
search for policies that would stretch the world’s effective supply for water allocation among uses (37). Other measures include
of water by promoting water conservation in irrigated agricul- reducing or converting nonbeneficial evaporation from soil or
ture. Our findings from the Rio Grande Basin suggest that water supply sources to beneficial crop ET, restricting acreage or water
conservation subsidies are unlikely to reduce water depletions by use expansion in cropped areas, switching to lower water-
agriculture under conditions likely to occur in many river basins. consuming crops, or irrigating current crops at a deficit (39, 40).
These findings suggest that some programs subsidizing irrigation Careful definition and administration of water rights can play
efficiency are likely to reduce water supplies available for a role. Water rights, water markets, water transfers, and water
downstream, environmental, and future uses. Although water accounting need to be defined in terms of water depleted, not
applied to irrigated lands may fall, overall water depletions just water applied. Without defining water use in terms of
increase. Our findings suggest reexamining the belief widely held depletions, individual farmers who invest in more efficient
by donors that increased irrigation efficiency will relieve the irrigation systems recognize that they apply less water per acre.
world’s water crisis. They may believe their water right is no longer fully used and may
The world’s single biggest water problem is scarcity (13). claim that the unused water is available for beneficial use. A
Reducing wet water scarcity requires accurate measurement of common reaction among private irrigators and even among
water use at different scales, including better estimates of return
flows and ET. It also requires defining water rights, water
**There are important cases where policies designed to reduce applied water successfully
transfers, water use, and water accounting overall in water reduce depletions. These occur where irrigation return flows travel to a saline body such
depletions rather than water applications. With better crops, as the ocean, a saline lake, or brackish groundwater. In these cases, most applied water
higher yields, and more even distribution of water, our results is consumptively used because unused irrigation water is lost for future freshwater use.
show that resulting crop water depletions increase. For example, Water-marketing efforts, such as those between southern California cities and Califor-
nia’s Imperial Irrigation District, which drains into the saline Salton Sea, have successfully
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in recent years crop yields have increased dramatically in the achieved water conservation in agriculture while providing incentives for more efficient
upper part of the Basin in southern Colorado. Alfalfa, potato, water use in all sectors from both local private and regional social views. We thank an
and grain yields in this part of the Basin have increased consid- anonymous reviewer for this insight.

Ward and Pulido-Velázquez PNAS 兩 November 25, 2008 兩 vol. 105 兩 no. 47 兩 18219
 public water conservation program administrators is to create a benefits of reduced return flows and seepage (12). This is a
new use of water or expand the current water use to a larger question facing water science, water policy, and water adminis-
number of acres or to higher water-consuming crops. The U.S. tration. Where reduced return flows and lost aquifer seepage
National Resources Conservation Service Environmental Qual- block another’s water use, conservation poses a serious question
ity Incentives Program (41) revolves around the premise that if for water rights administration because those effects are often
irrigators install a more efficient irrigation system and irrigate 2 hard to measure and often occur with considerable delay.
parcels instead of 1 with the same water right, increased effi- Answering this question requires sorting out conflicting impacts
ciency in water use results. Water rights administrators can guard of water application versus water depletion and an understand-
against this error. Where water rights are administered based on ing of the transmission of those effects at the basin scale.
water depletions, water right administrators will not permit
investors in irrigation efficiency to presume that water is saved. ACKNOWLEDGMENTS. We thank David Molden, Robert Young, Chris Perry,
Indeed, where hydrologic realities of a river basin are imple- Mobin-ud-Din Ahmad, Ted Sammis, Ray Huffaker, Phil King, Steve Vandiver,
mented into law, the right to acreage farmed and to water Munir Hanjra, and Grant Cardon for valuable comments on earlier drafts. We
applied will be reduced after measures are taken to increase also thank two reviewers for their insightful comments. A talk given by
Richard Allen at a 2007 New Mexico State University Water Lecture Series
irrigation efficiency. provided additional important insights. This work was supported by the Rio
A major question for efficient public policy is whether or not Grande Basin Initiative and by the New Mexico Agricultural Experiment
the increase in net farm income compensates the forgone Station.

1. Easterling (2007) Climate change and the adequacy of food and timber in the 21st 23. Bastiaanssen WGM, Bandara KMPS (2001) Evaporative depletion assessments for
century. Proc Natl Acad Sci USA 104:19679. irrigated watersheds in Sri Lanka. Irrig Sci 21:1–15.
2. Postel SL, Daily GC, Ehrlich PR (1996) Human appropriation of renewable fresh water. 24. Vaux HJ, Howitt RE (1984) Managing water scarcity: An evaluation of interregional
Science 271:785–788. transfers. Water Resource Res 20:785–792.
3. Bouwer H (2002) Integrated water management for the 21st century: Problems and 25. Booker JF (1995). Hydrologic and economic impacts of drought under alternative policy
solutions. J Irrig Drain Eng 128:193–202. responses. Water Resource Bull 31:889 –906.
4. Gordon LJ, et al. (2005) Human modification of global water vapor flows from the land 26. Hurd BH, Callaway JM, Smith JB, Kirshen P (2002) (2004) Climate change and US water
surface. Proc Natl Acad Sci USA 102:7612–7617. resources: From modeled watershed impacts to national estimates. J Am Water
5. Gupta SK, Deshpande RD (2004) Water for India in 2050: First-order assessment of
Resource Assoc 40:129 –148.
available options. Curr Sci 86:1216 –1224.
27. Ward FA, Booker JF, Michelsen AM (2006) Integrated economic, hydrologic, and
6. Plusquellec H (2002) Is the daunting challenge of irrigation achievable? Irrig Drain
institutional analysis of policy responses to mitigate drought impacts in the Rio Grande
51:185–198.
Basin. J Water Resource Plan Manage 132:488 –502.
7. Oster JD, Wichelns D (2003) Economic and agronomic strategies to achieve sustainable
28. Ward FA, Pulido-Velázquez M (2008) Incentive pricing and cost recovery at the basin
irrigation. Irrig Sci 22:107–120.
8. Gleick PH (2002) Global freshwater resources: Soft water paths. Nature 418:373. scale. J Environ Manage, in press.
9. English MJ, Solomon KH, Hoffman GJ (2002) A paradigm shift in irrigation manage- 29. Ward FA, Pulido-Velázquez M (2008) Efficiency, equity, and sustainability in a water
ment. J Irrig Drain Eng 128:267–277. quantity– quality optimization model in the Rio Grande Basin. Ecolog Econ 66:23–37.
10. Tilman D (1999) Global environmental impacts of agricultural expansion: The need for 30. Ward FA, Booker JF (2003) Economic costs and benefits of instream flow protection for
sustainable and efficient practices. Proc Natl Acad Sci USA 96:5995– 6000. endangered species in an international basin. J Am Water Resource Assoc 39:427– 440.
11. Schultz B, De Wrachien D (2002) Irrigation and drainage systems research and devel- 31. Booker JF, Young RA (1994) Modeling intrastate and interstate markets for Colorado
opment in the 21st century. Irrig Drain 51:311–327. River water resources. J Environ Econ Manage 26:66 – 87.
12. Rockstrom J, Lannerstad M, Falkenmark M (2007) Increasing water productivity 32. Draper AJ, Jenkins MW, Kirby KW, Lund JR, Howitt RE (2003) Economic engineering
through deficit irrigation: Evidence from the Indus plains of Pakistan. Proc Natl Acad optimization for California water management. J Water Resource Plan Manage
Sci USA 104:6253– 6260. 129:155–164.
13. Jury WA, Vaux HJ (2006) The role of science in solving the world’s emerging water 33. Pulido-Velázquez M, Jenkins MW, Lund JR (2004) Economic values for conjunctive use
problems. Proc Natl Acad Sci USA 102:15715–15720. and water banking in southern California. Water Resource Res 40:W03401.
14. Jensen ME (2007) Beyond irrigation efficiency. Irrig Sci 25:233–245. 34. Booker JF, Michelsen AM, Ward FA (2005) Economic impact of alternative policy
15. Bohannon J (August 21, 2006) Not a drop to drink. Science Now Daily News, p 821. responses to prolonged and severe drought in the Rio Grande Basin. Water Resource
16. Hussain I, Turral H, Molden D, Ahmad MD (2007) Measuring and enhancing the value Res 41:W02026.
of agricultural water in irrigated river basins. Irrig Sci 25:263–282. 35. Huffaker R (February 19, 2007) When conserving water actually doesn’t. Sci Mag News.
17. Huffaker R, Whittlesey N (2000) The allocative efficiency and conservation potential of
36. Ahmad MD, Giordano M, Turral H, Masih I, Masood Z (2007) At what scale does water
water laws encouraging investments in on-farm irrigation technology. Agric Econ
saving really save water? Lessons from the use of resource conservation technologies
24:47– 60.
in Pakistan. J Soil Water Conserv 62:29A–35A.
18. Peterson JM, Ding Y (2005) Economic adjustments to groundwater depletion in the high
37. Molden D (2007) Water For Food, Water For Life: A Comprehensive Assessment of
plains: Do water-saving irrigation systems save water? Am J Agric Econ 87:147–159.
Water Management in Agriculture (Earthscan, London).
19. Huffaker R, Whittlesey N (2003) A theoretical analysis of economic incentive policies
38. Lubchenco J (1998) Entering the century of the environment: A new social contract for
encouraging agricultural water conservation. Water Resource Dev 19:37–55.
20. Scheierling SM, Young RA, Cardon GE (2006) Public subsidies for water-conserving science. Science 279:491– 496.
irrigation investments: Hydrologic, agronomic, and economic assessment. Water Re- 39. Fereres E, Soriano MA (2007) Deficit irrigation for reducing agricultural water use. J Exp
source Res 42, 10.1029/2004WR003809. Bot 58:147–159.
21. Doorenbos J, Kassam A (1979) Yield Response to Water (Food and Agricultural Orga- 40. Sarwar A, Perry C (2002) Increasing water productivity through deficit irrigation:
nization, Rome). Evidence from the Indus plains of Pakistan. Irrig Drain 51:87–92.
22. Perry C (2007) Efficient irrigation, inefficient communication, flawed recommenda- 41. Natural Resources Conservation Service (2008) Environmental Quality Incentives Pro-
tion. Irrig Drain 56:367–378. gram (Available at: www.nrcs.usda.gov/programs/farmbill/2002/products.html).
Downloaded by guest on February 10, 2020

18220 兩 www.pnas.org兾cgi兾doi兾10.1073兾pnas.0805554105 Ward and Pulido-Velázquez